First off, you should be able to get the past *thirty* days' worth. However, I don't think that's the real question.
I've been keeping copies of the jigsaw sudokus almost since I started there, which takes us back to about...2007? 2008? Something like that. Back then, if you went on holiday, you either had to bow out of the lists or go crazy trying to find a place to access the site, for it was not possible to do puzzles in advance.
When they first began advance puzzles, it was briefly possible to access their entire back collection. Unfortunately, some people discovered that they could do them, upload them, and jigger their scores. So, not unreasonably, the people running the site went back to locking all but the previous thirty-day's-worth. Fortunately, with all the hoo-ha on the forums, I guessed in time that they'd do this; so I hurriedly saved *all* the daily jigsaws. One by one--it took ages. It meant, though, that I have a complete set. (For a while, there, I had a lot of fun, as you can imagine.)
At that time, I didn't bother saving the extremes since I'd never been able to solve one without bifurcating. However, over time one *does* improve; and nowadays I guess I can solve them about 20% of the time. That, of course, meant that I wished I'd collected all of those as well.
A few months ago, I did discover a way to get in the back door using the Wayback Machine, and collected all the weeky Extreme Jigsaws as well. If you want to try it:
1. Go to the advance puzzles, get the *print* version for one of the future Extreme Jigsaw sudokus.
2. Go to the Wayback Machine (http://archive.org/index.php
). Cut'n'paste the URL of the advance sudoku in the box, and hit "Take Me Back".
3. This will get you to a page that has the future puzzle. At the top, it will say the Internet Archive doesn't have a copy, and is getting it off the live web.
4. Note that, just above this message, there is a small box with the URL of the page. (I am NOT referring to your browser's own box.)
5. At this point, you have to be canny. To get a past puzzle, you have to alter the date; but, as you are dealing with weeklies, not all dates will work. I *can* tell you that 2008-04-12 will work. From there, you can work backwards and forwards by 7s. (The puzzle for 2008-04-12 was #81, by the way.)
6. When altering the date, *only* change the very end of the URL in the box, the bit that codes the date.
Sadly, this doesn't seem to work for the Dailies. You just get the usual error message. (Sorry.)